How can I, make a Login Script?

How can I make a Login Script? What I am saying is a script that would make a account for a user, and they can use that account on guest and others? Is this even possible? Also, how would I create a script or something that would allow the user to put in letters in numbers?

Im not sure this is even possible, And if it was would need one heck of a lot of scripting.

You mean like the play to login from his account in-game?

Nope possible.